In a wireless LAN communication, a sleep mode may be used to reduce power consumption of a communication terminal. This technology is defined in ETSI TS 101 761-2 [5.2.6] (HiperLAN2) and ARIB STD-T70 [6.2.2.4] (HiSWANa).
More specifically, as shown in FIG. 1, before a sleep mode is entered, a communication terminal apparatus (MT) sends a sleep request to a communication terminal accommodation apparatus (AP) first. In response to the sleep request, the AP checks with the MT to see whether or not to start the sleep mode. After receiving a confirmation of the sleep mode from the AP, the MT enters the sleep mode.
In the sleep mode, there are periods during which the MT checks a BCH (broadcast channel) and the MT checks the BCH at this timing and when there is uplink or downlink data, the MT returns from the sleep mode to a normal mode and transmits/receives data. When there is no more data again, the MT enters the sleep mode using the above described procedure as required.
As in the case of an Internet telephone, when an application extends over not so wide a band and has isochronous data to be transmitted periodically, it is possible to achieve power saving by entering a sleep mode. As shown in FIG. 2, if a procedure such as a sleep request and confirmation is carried out every time, overhead 1101 necessary for the procedure increases, which causes a problem that the efficiency of power saving deteriorates due to the sleep mode and the next data communication starts before the sleep procedure is taken, thus preventing the sleep mode from being actually entered in the worst case.